(1) Field of the Invention
The present invention relates to a magnetic disk drive in which a motor coil for moving a magnetic head carrier is energized with a small current to release the adhesion on the magnetic head by an adhesion control circuit in the drive circuit for driving the motor before the rotation of the magnetic disk, and which is able to use smaller and cheaper transistors for the motor drive amplifier in a drive circuit, thereby reducing power consumption.
(2) Description of the Related Art
Magnetic disk drives are devices in which a magnetic head is positioned on a specific track of a rotating magnetic disk, in order to read data from, or write data to that track. The magnetic head floats on the surface of the disk because of the air flowing over it via the rotation of the disk, and thus the head can perform non-contact read-write operations. When the magnetic disk is not rotating, the head is touching the magnetic disk.
Presently, most magnetic disk drives employ a so-called CSS or "Contact Start Stop" system in which the head contacts the disk surface when the disk is not rotating. This system is practical because miniaturization of the head has reduced the amount of pressure on the disk from the head. The use of much cleaner air in the disk housing and the use of a lubricant also aid in making the system practical. The lubricant reduces dynamic friction between the head and the disk when starting and stopping the rotation of the disk and reduces damage if the head either crashes onto the disk due to mechanical shock or the head forces dust into the disk.
However, because heads are continuing to be further miniaturized, and because the finish of both the head and disk surfaces are continuously being made smoother, the head tends to adhere to the disk surface when the disk is not being rotated. This adhesion is caused by a kind of attractive force which can occur between two mirror smooth surfaces. This adhesion becomes stronger with presence of the lubricant, and would cause serious damage to the head, its suspension structure or the disk when the magnetic disk is rotated, if not released properly.
For this reason, before starting to rotate the magnetic disk, the adhesion must be released by pulling the magnetic head in the radial direction of the magnetic disk. To ensure the release of the adhesion before starting to rotate the disk, conventional magnetic disk drives employ a specific release mechanism. This mechanism moves a head actuator along the radial direction of the disk before the disk starts to rotate. Since the suspension structure gimbals have enough stiffness in the radial direction, the head can be released from the adhesion without causing any damage to the gimbals.
Several ways of moving the head have been proposed. In U.S. Pat. Nos. 4,530,021 and 4,589,036 the head is supplied with an alternating current to cause "micromotion" when starting rotation of the disk. Further, in U.S. Pat. No. 4,589,036, actual movement of the head is sensed and the "micromotion" is controlled thereby. However, these methods require a precisely controlled alternating current generator and sophisticated sensing circuits.
Another method, which uses a much simpler circuit, is disclosed in Japanese Unexamined Patent Publication No. 61-198480 (published Sept. 9, 1986). In this method, when the magnetic disk drive is stopped, the head actuator is positioned, close to a stopper means. The stopper means restricts the actuator movement and comprises an elastic material. Upon starting up the disk drive, the head actuator is moved towards the stopper and compresses the elastic material. This causes the head to be slightly offset in the radial direction before the disk actually begins to rotate. This method requires only a head actuator drive current large enough to compress the elastic material. A square waveform is used as the drive current, because the movement of the actuator is safely restricted by the stopper.
However, the inventor of present invention has discovered that the above described method requires a high power consumption transistor in an amplifier for energizing the coil of the head actuator motor, thereby making the amplifier larger in scale, higher in price, and greater in power consumption.